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Downsizing with Direct Injection and Turbocharging Is the Future of Gasoline Engines

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Downsizing with Direct Injection and Turbocharging Is the Future of Gasoline Engines

The 1.6-liter turbocharged GDI I4 engine scheduled to be inside the upcoming 2013 Veloster Turbo produces 201 HP at 6000 rpm and 195 lb-ft of torque from 1750 – 4500 rpm. And it does so on regular unleaded.

The Veloster Turbos 1.6L GDI-T is currently estimated to deliver a 27/38 mpgUS city/highway when mated to Hyundai slick shifting 6-speed. The engine features a twin-scroll turbocharger that when combined with the GDI system, results in almost instantaneous power delivery. Hyundai has brought this technology down its line-up from the award winning Sonata 2.0T.

Hyundai’s twin-scroll turbo in explicit detail

Twin-scroll turbochargers designs have two exhaust gas inlets divided by split walls inside the turbine housing, with both gas passages controlled by a waste-gate. A twin-scroll turbo recovers even more energy from the exhaust than a single-scroll turbocharger, thanks to a divided manifold. The twin-scroll design separates the cylinders whose exhaust gas pulses interfere with each other, resulting in improved pressure distribution in the exhaust ports and a more efficient delivery of exhaust gas energy to the turbocharger’s turbine.

At the start of the intake stroke of cylinder one and when both the intake and exhaust valves of cylinder one are open (valve overlap period), cylinder three already starts its exhaust stroke with the exhaust valve open. If the exhaust passages of cylinder one and three were connected, the exhaust gas pulse from cylinder three would increase the back pressure of cylinder one. This would reduce the induction of the fresh air and increase the amount of hot residual gases inside the cylinder. With the twin-scroll turbocharger setup, the interference is minimized.

The result of this superior scavenging effect from a twin-scroll design leads to better pressure distribution in the exhaust ports and a more efficient delivery of exhaust gas energy to the turbocharger's turbine. This in turn allows greater valve overlap, resulting in an improved quality and quantity of the air charge entering each cylinder. In fact, with more valve overlap, the scavenging effect of the exhaust flow can literally draw more air in on the intake side. At the same time, drawing out the last of the low-pressure exhaust gases help pack each cylinder with a denser and purer air charge. Maximum boost from the turbocharger is 18 psi.

The twin-scroll turbocharger design has several other advantages over traditional, single-scroll turbocharging systems, including:

Improved combustion efficiency

Low engine-speed efficiency

Kinetic exhaust gas energy is not wasted or trapped

Cooler cylinder temperatures

Lower exhaust temperatures

Leaner air/fuel ratio

Better pressure distribution in the exhaust ports and more efficient delivery of exhaust gas energy to the turbocharger's turbine

GDI

The GDI fuel delivery system contributes to improved fuel efficiency and lower emissions. This shorter, more direct path of fuel delivery allows for greater control of the fuel mixture at the optimum moment, thus improving efficiency. The fuel is injected by a camshaft-driven, high pressure pump that operates at pressures up to 2175 psi. Direct injection also utilizes a higher-than-normal compression ratio, while achieving a best-in-class 125.6 horsepower-per-liter in the Veloster Turbo.

By 2016, the number of hyper-efficient gasoline fueled I4s will increase by 20 percent to more than 20 million units globally. Based on this trend, most every automaker will offer a turbocharged gasoline engine.

At 201 HP the GDI is significantly above the Civic HF and most of the others. If Hyundai chose to make a 1.2L with 140/128 hp/torque it may well beat the Civic HF. Hyundai may be betting on more sales to people wanting power and good economy. Sorta like diesels where people pay a big premium not expecting a payback, but power with economy. No doubt not all engine design groups are getting equal results, but Turbo and DI seems to have promise.